You shouldn't download updated plugins and update them manually by dropping jar files, it should show on the plugins page that update is available (if it is required, sometimes just plugin version number is bumped to fix some issues with the site). If you really want to reload a plugin, then you should remove and install it via Admin Console (uninstall and install with a plus sign).
Now about the actual problem. What operating system? What installer for Openfire do you use? If it is Win Vista or later are you running it via Openfire Launcher? If so, do you run it with Run as administrator option? Maybe you use some non Oracle Java or do you use Openfire's built-in Java?